Conventionally, such a printing apparatus has been known widely that forms an image such as a photograph of face and character information on a printing medium such as a plastic card. In such a printing apparatus, an indirect printing scheme is used in which an image (mirror image) is formed on a transfer film (recording medium) with a thermal head via an ink ribbon, and next the image formed on the transfer film is referred to a printing medium.
This type of printing apparatus has conventionally detected a remaining amount of the ink ribbon by detecting the diameter of the supply spool or wind-up spool. For example, Patent Document 1 discloses techniques for detecting passage of a Bk (Black) panel (surface) with a sensor, and detecting a remaining amount of the ink ribbon from how many times the spool rotates during the period. In other words, when it is assumed that the length of the Bk panel is 98 mm, it is detected how many times the spool rotates for a period during which the Bk panel is transported 98 mm. Since the rotation amount is smaller as the diameter is thicker, while being larger as the diameter thinner, the diameter of the spool is calculated from the rotation amount.